Can someone give me an in-depth explanation why Summoner is arguably the worst DPS?

[Bigcat9715]

I may not like blm playstyle much, but I just have a feeling that kind of rotation is not ideal. Relying on a proc with 40% chance just save some mp bothers me for some reason. Wouldn't just casting fire 3 till you have to switch to blizz 3 and thunders net a more constant dps with a higher average over hoping you get a firestarter? Idk, I never liked blm and only leveled it for swiftcast so don't take me for an authority on it.

I've just fully leveled my BLM, and let me tell you, if you have 3 stacks of Astral fire you don't want to waste your time and mp on casting magic that cost 1058 a shot when you can get it for free. Plus you have a overwhelming chance of getting a fire 3 every rotation. You can get it a couple of times every rotation. BLM's dps is ridiculous.